A graphene nanoribbon is known as one of nanocarbon materials. In view of application of a graphene nanoribbon to semiconductor devices such as field effect transistors, there is an attempt to control its width and edge structure so as to obtain a semiconducting graphene nanoribbon having a band gap. For example, an armchair edge or a chiral edge is known as an edge structure of a semiconducting graphene nanoribbon.
See, for example, the following documents:    International Publication Pamphlet No. WO2013/061258; and    Verónica Barone, Oded Hod, and Gustavo E. Scuseria, “Electronic Structure and Stability of Semiconducting Graphene Nanoribbons”, Nano Letters, Vol. 6, No. 12, pp. 2748-2754, 2006.
Applying a graphene nanoribbon to a semiconductor device does not always result in a high performance semiconductor device. The reason for this is that it is difficult to obtain a graphene nanoribbon having a shape and characteristics, such as a band gap, suitable for the semiconductor device.